Strengthened, light weight wallboard and method and apparatus for making the same

ABSTRACT

A novel wallboard composition is disclosed comprising a unique combination of synthetic binders selected for their ability to establish a strengthened permanent bond in the final dry state in combination with an expanded mineral such as Perlite which largely reduces the amount of gypsum over current gypsum wallboard formulations, thus reducing the weight while maintaining the strength of the wallboard structure. In a preferred embodiment, the lightweight, strengthened wallboard of the present invention also comprises a covering veneer that is applied to the top ply of the face paper to provide increased strength, moisture resistance, and fire retardency, and the back paper top ply is treated to provide increased flexural strength. Additionally, this invention relates to the unique manufacturing process to produce the wallboard composition of the present invention in order to create a lightweight, strengthened, moisture resistant, and fire retardant wallboard used to cover walls and ceilings in construction applications. Still further, this invention relates to the apparatus for manufacturing the wallboard composition of the present invention, including a method and apparatus for economically converting a standard gypsum wallboard manufacturing facility into a facility for manufacturing wallboard of the present invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 09/374,589, filed: Aug. 13, 1999 by the inventorherein and entitled “STRENGTHENED, LIGHT WEIGHT WALLBOARD AND METHOD ANDAPPARATUS FOR MAKING THE SAME,” which application in turn is based uponand gains priority from U.S. Provisional Patent Application Ser. No.:60/139,618, filed: Jun. 17, 1999 by the inventor herein and entitled“IMPROVED WALLBOARD AND METHOD AND APPARATUS FOR MAKING THE SAME,” andis also a Continuation-in-Part Application of U.S. patent applicationSer. No. 09/195,438, filed Nov. 18, 1998 by the inventor herein andentitled “LIGHT WEIGHT FIRE AND MOISTURE RESISTANT WALLBOARD.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to new “drywall” compositions and methods formaking the same that are useful in the manufacture of wallboard forcovering walls and ceilings in construction applications. Moreparticularly, this invention is directed to a novel wallboardcomposition comprising a unique combination of synthetic bindersselected for their ability to establish a strengthened permanent bond inthe final dry state, in combination with an expanded mineral such asPerlite which largely reduces the amount of gypsum present in thewallboard product from what has been required by previous gypsumwallboard formulations. This reduction in the amount of gypsum presentin the wallboard formulation in turn reduces the weight of the wallboardstructure while maintaining its strength. Moreover, the syntheticbinders uniquely cross-link with the expanded mineral to form a muchstronger bond between the constituent components of the wallboard corematerial than that which has been available in previously utilized orknown wallboard products. In a preferred embodiment, the lightweight,strengthened wallboard of the present invention also comprises acovering veneer that is applied to the top ply of the face paper toprovide increased strength, moisture resistance, and fire retardency,and the back paper top ply is treated to provide increased flexuralstrength. Additionally, this invention relates to the uniquemanufacturing process to produce the wallboard composition of thepresent invention in order to create a lightweight, strengthened,moisture resistant, and fire retardant wallboard used to cover walls andceilings in construction applications. Still further, this inventionrelates to the apparatus for manufacturing the wallboard composition ofthe present invention, including a method and apparatus for economicallyconverting a standard gypsum wallboard manufacturing facility into afacility for manufacturing wallboard of the present invention.

2. Description of the Background

Conventional gypsum drywall has been utilized for approximately the pastfifty years in the construction industry with gypsum comprising theprimary core ingredient The manufacture of gypsum drywall is presentlyan expensive, complex, difficult, and tightly controlled manufacturingprocess. The gypsum wallboard manufacturing process today entailsseveral elaborate steps with significant environmental concerns, bothinternally and externally, regarding the product itself and themanufacture thereof. An increasingly shortened supply of domestic gypsumrock remains available today, which has necessitated the development andusage of synthetic gypsum as a substitute. However, the production ofsynthetic gypsum requires an extremely complex synthetic gypsumproduction facility. Such facilities include FGD (flu gasdesulferization) gypsum production plants which are required by thenature of the manufacturing process to be located next to power plantfacilities. These power plants utilize high sulfur coal, which ispredominate in the Eastern United States, to generate power. The wasteproduced by these power plants is classified and desulferized intosynthetic gypsum. This synthetic gypsum is then calcined and used as asubstitute for natural gypsum for use in the wallboard manufacturingprocess. Given the significant risk of detrimental long-term healtheffects of a waste slag and coal product, the processing and use of suchsynthetic gypsum has also fueled environmental concerns. It is an objectof the present invention to provide a new and distinctly differentenvironmentally safe class of wallboard for use in the constructionindustry that utilizes environmentally friendly synthetic adhesives.

The continuously depleting supply of gypsum coupled with the risingdemand for wallboard products has caused the price of gypsum andgypsum-based products to rise substantially over recent years. In thefield of gypsum wallboard composition, relatively low prices ofmaterials have kept the core of gypsum wallboard unchanged for thebetter part of the 20th century. However, given the booming constructionindustry and the increasing demand for housing, the demand for wallboardproducts has significantly exceeded the available manufactured supply ofwallboard. This increased demand has dramatically driven the costs ofwallboard products upward. Likewise, the need to supplement the naturalgypsum wallboard products with the more costly synthetic gypsum productshave also driven up the costs of wallboard products. These increasingcost factors have established a need for a lightweight, strengthened,and re-engineered wallboard product that minimizes the amount of gypsumpresent in the wallboard formulation.

Attempts have been made in the past to both strengthen and lightentraditional wallboard products, but such efforts have evidenced theaddition of substantial costs to the finished product. For example,attempts have been made in the past to use a very low percentage of aninorganic or synthetic binder in wallboard formulations, typically 1% to2%, in an effort to slightly effect the strength of the wallboardproduct. However, the amount of binder required to substantiallyincrease strength and remain cost effective has not been realized. Asdisclosed herein and as a part of the present invention, it has beenfound that by placing the equipment needed to polymerize the basecomponents of the synthetic binder on-site at the wallboardmanufacturing facility, manufacturing costs may be greatly reduced.

Modern gypsum wallboard manufacturing facilities are very expensive inand of themselves, comprising numerous pieces of complex manufacturingand material handling equipment. Traditionally, the removal of thegypsum rock from gypsum mines or quarries is more difficult than stripor surface mining the softer Perlite ore from the mountain or ranges.After mining, the harder and larger gypsum rocks are crushed and reducedto smaller sizes and conveyed to where these smaller rocks are crushedinto tiny particles. Next, the crushed gypsum is processed through acomplex Calcining system involving a roller mill, a Calcining kettle, animp mill and/or GC mill to reduce the gypsum fines into a chalk-likegypsum aqueous slurry. This Calcining system and process is expensive asit involves flash-drying and heating the gypsum land plaster or gypsumslurry in order to remove much of the water from the material. Followingthis dehydration process, the gypsum stucco is stored in holding binsand fed into equipment such as a pin mixer and a screw type conveyer.Water is again added along with other ingredients such as foams,starches, cementious materials and other chemicals to form the finalprepared gypsum slurry. The gypsum paste is then spread onto andcompressed between facing and backing paper and is cut further down theline. Next, a complex high temperature kiln dries the green gypsum boardfor approximately one hour or more, which is begun at lower temperatures(approximately 250° F.), then to a higher temperature (approximately600° F.), and down again to exit from the kiln at lower temperatures(approximately 200° F.), leaving the gypsum board virtuallymoisture-free. This complex system of processing and material handlingequipment is extremely expensive, such that the start-up of a newfacility to manufacture a new type of wallboard has in the past beencost prohibitive. It would therefore be advantageous to provide a meansby which an existing manufacturing facility could be modified at littleexpense to produce a strengthened and lighter weight wallboard product.

Perlite and other minerals have previously been used in wallboardconstruction as a filler, and has likewise been used in a variety ofother industrial uses, including abrasives, acoustical plaster and tile,charcoal barbecue base, cleanser base, concrete construction aggregates,filter aid, fertilizer extender, foundry ladle covering and sandadditive, inert carrier, insulation board filler, loose-fill insulation,molding filler medium, packaging medium, paint texturizer, propagatingcuttings for plants, refractory products, soil conditioner, tile mortaraggregate, and lightweight insulating concrete for roof-decks. Perliteis a glassy volcanic rock having the unusual characteristic of expandingto about 20 times its original volume when heated to an appropriatetemperature within its softening range. The resultant expanded productfinds a variety of industrial and constructional applications owing tothe material's low density with attendant properties of low thermalconductivity and high sound absorption.

Petrographically, Perlite can be described as a glassy, volcanic,rhyolitic rock having a pearl-like luster and usually exhibitingnumerous concentric cracks resembling an onionskin in appearance.Chemically, crude Perlite is essentially a metastable amorphous aluminumsilicate. A typical average chemical analysis of Perlite would show arange of 71% to 75% SiO₂, 12.5% to 18.0% Al₂O₃, 4 to 5 percent K₂O, 1%to 4% sodium and calcium oxides, and minor amounts (traces) of metaloxides. Perlite is chemically inert and has a pH of approximately 7. Thespecific gravity of Perlite ranges from 2.2 to 2.4 (139 to 150 poundsper cubic foot) and has hardness between 5.5 and 7 (Mohs' scale). CrudePerlite may range from transparent light gray to glassy black in color;however, the color of Perlite when expanded will range from snowy whiteto grayish white.

Commercially, the term “Perlite” also includes the expanded product.When particles of Perlite are heated to a soft consistency, the combinedwater present (2% to 5%) in the glass vaporizes, forming steam thatexpands each particle into a mass of glass foam. The original volume ofthe crude Perlite may be expanded 4 to 20 times at temperatures between1,200° F. and 2,000° F. Expanded Perlite may be a fluffy highly porousmaterial or may be composed of glazed glassy particles having a lowporosity. Dependent upon the inherent physical properties and processingvariables, the bulk weight of expanded Perlite usually ranges from 2 to20 pounds per cubic foot.

Specifications have been established by the American Society for Testingand Materials (ASTM) for the sizing and bulk density of expanded Perliteaggregate used for plaster and insulating concrete. Perlite for filtermedia uses and for many other uses usually follows specifications forproper sizing and other properties recommended by producers.

Perlite (expanded) can be graded by density in pounds per cubic foot,and classified by product number or trade name for producer and useridentification. The expanded product can weigh as little as 2 pounds percubic foot, but the most widely used bulk-density grade range is from 7to 15 pounds per cubic foot. The range of expanded Perlite utilized inthe wallboard composite core of the present invention is 4 to 10 poundsper cubic foot. Grades typical to this range include concrete, plaster,and cavity fill or masonry. The particle size ranges from 100 to 2,000microns.

The expanded product is bagged for shipment and generally will be involume of 4 cubic feet per bag. The expanded product is generallyshipped via truck or rail. If by rail, the expanded product may beshipped in bulk dry density designed transport cars.

Expanded Perlite, depending on the expansion process and the grade ofPerlite, can affect the expanded weight and can be used in theproduction of many products where weight is an important factor. In theconstruction industry, Perlite's incombustibility and low waterabsorption make it a superior insulating material. Perlite plasteraggregate is used extensively to fireproof structural steel constructionand to reduce the weight of interior walls and ceilings. Perliteconcrete aggregate roof-decks also insulate and save weight. ExpandedPerlite is an important component of roof insulation (gypsum) board,masonry (cavity fill), and floor and wall tiles.

Some of the many important applications of Perlite include its use as aninsulator (in cryogenic technology) to hold solidified gases such asliquid oxygen at extremely low temperatures, to absorb oil spills onwater and wet surfaces, to clean up effluents containing oily wastes,and as an additive in molding sands.

In sum, while perlite has found a variety of uses in the constructionindustry, and even as a filler in wallboard products, it has notheretofore been effectively employed as a catalyst for significantlyreducing the amount of gypsum required in the wallboard formulation.

Further, the green and/or gray-colored facing and backing paper used onstandard gypsum wallboard is commonly low-grade and recycled, andperforms poorly under rainy or wet surface conditions during shipping,construction, and the installation process. Weight factors of the gypsumdrywall/sheetrock, as commonly termed, have been an ongoing concernduring transportation and installation, as have general safety issues,particularly in hanging ceiling boards. Breakage and loss of material isan adverse factor during brittle gypsum board installation. It wouldtherefore also be advantageous to provide an improved facing and backingpaper lacking the shortcomings evident in the prior art.

3. Description of the Prior Art

The use of the main ingredient, calcium sulfate hemihydrateC_(A)SO₄•2H₂O, in the manufacture of gypsum wallboard and its relatedproducts has predominately been unchanged or unchallenged in its basecomponents for over half a century. It has long been a conventionalpractice to finish the interiors and exteriors of buildings with gypsumcore construction materials such as wallboard, lath, or sheathing. Ingeneral, these boards comprise essentially a core of set interlacedgypsum crystals disposed between fibrous, especially paper, linersheets. After the gypsum slurry has set (i.e., reacted with the waterfrom the aqueous slurry) and dried, the sheet is cut into standardwallboard sizes. Methods for the production of gypsum drywall aredescribed, for example, in the Kirk-Othmer Encyclopedia of ChemicalTechnology, Second Edition, 1970, Vol. 21, pages 621-24, the disclosureof which is hereby incorporate herein by reference.

It has been known to incorporate certain additional agents in the coreof gypsum wallboard. These have included, for example, foam aggregatewherein a foam has been shredded to a rough consistency and thenincorporated into the gypsum slurry prior to forming and settingthereof. Also, expanded mineral fillers such as perlite and/orvermiculite have been incorporated into the gypsum slurry in smallamounts from 0.5 to 10 percent, in addition to organic adhesives such asstarch or dextn, or other fibers. Other agents have also been added,including simple chemicals which react within the gypsum slurry to formgasses. For example, carbonates are added to yield CO₂ within theslurry; likewise, other air entraining agents, such as soap foams, maybe employed to enable whipping air into the gypsum slurry during mixing.

Unfortunately, however, the amount of air or gas cells, or voids, whichcan be incorporated is limited, because the strength of the compositewallboard core is reduced when the amount of air cells is increasedbeyond a certain point. Likewise, the ability of the board to withstanda nail pull through the board is adversely effected by excessive airentraining. Additionally, historically expanded minerals were not addedin gypsum wallboard beyond 2 to 3 percent because strength tests weresignificantly reduced, in both nail pull and flexural break tests,according to ASTM C79 and ASTM C473. While it has been an intention ofindividual inventors and major manufacturers to produce a lightweight,strengthened, and essentially improved wallboard product over currentformulations, the problem of providing a wallboard product withincreased strength while reducing its weight at a relative low cost hasnot been practically realized, either in re-engineering the wallboarditself or the manufacturing process thereof. Many combinations andcompositions have been tried and tested in the past, but many remainunutilized due to impractical applications and/or significant increasesin production costs. Reduced weight and density boards should meet orexceed industry standards and have strengths equal to or greater thantheir heavier counterparts according to ASTM standards. Such lightweightwallboard compositions should be able to be manufactured usingconventional high-speed manufacturing apparatus and not suffer fromother negative side effects of a completely different manufacturingprocess.

The addition of synthetic binders has very recently been attempted asdisclosed in U.S. Pat. No. 5,879,825 to Burke et al.; however, theengineering and chemical research in various combinations of complexchemical formulations and combinations thereof has been quite limited.Additionally, the environmental concerns of noxious fumes under fireengineering standard ASTM testing E119 were not realized or considered,and cost considerations limited the amount of acrylic polymer to 1 to 2percent, such that a polymer having a minimal cross-linking performanceresulted. Further, while the use of Perlite as an antidessicant toprevent the dehydration of gypsum crystals formed during setting of thecore composition is disclosed, no consideration is given to introducingan expanded mineral, such as perlite, as a substitute for gypsum as oneof the structural foundations of the wallboard core, nor the specificneed for a synthetic binder composition for establishing a completecrosslinking between the constituent elements of the wallboard core inorder to create a molecular change within the strengthening agent, whichmolecular change is in turn required to completely bond a substantiallyreduced amount of gypsum with the other components of the wallboardcore. Likewise, Burke et al. '825 discloses the use of its“strength-enhancing agent” only in the amount of 0.25 percent to about2.5 percent solids, thus greatly limiting the cross-linking effect ofthe agent and the ability to significantly reduce the weight of thefinished wallboard product

Other attempts have been made in the prior art to provide adhesivecompositions for use in bonding cellulosic and other porous materials.For example, U.S. Pat. No. 3,720,633 to Nickerson discloses a polyvinylalcohol-based adhesive composition for use in paper convertingapplications. However, once again, no mention or suggestion is made ofthe need for a specific synthetic adhesive composition able to establisha sufficient cross-linking between its components to bind with gypsumand/or an expanded mineral to create a core material having the strengthcharacteristics necessary to utilize the material as a wallboard sheet,while having a reduced weight over compositions that have beenpreviously known.

Still further, U.S. Pat. No. 5,534,059 to Immordino, Jr. discloses amachinable plaster composition comprising a polymer-modified, gypsumbased material, including a water redispersable powder polymer binder.However, in this instance, the polymer binder is used to produce a muchmore rigid, and thus easily machinable, plaster blank for use inconjunction with computer aided milling machines than previouscompositions, and once again fails to disclose or suggest anycombination which might be used to produce a strengthened yetlightweight wallboard having a synthetic binder which is fullycross-linking in order to establish a rigid bond with the gypsum and/orexpanded mineral constituents of the wallboard core.

It would therefore by highly advantageous to provide a high strength,lightweight wallboard product which reduces the need for gypsum in thewallboard composition, and which utilizes a synthetic binder compositionthat enables a complete cross-linking of the constituent elements of thewallboard core to form a rigid structure with the structural integrityto withstand the structural requirements of traditional wallboardproducts. Such wallboard products should meet industry requirements, andlikewise have a strength at least equal to previously known wallboardproducts while reducing the weight of the finished wallboard sheet. Suchwallboard should also have the ability of being manufactured atexisting, traditional gypsum wallboard production facilities withoutrequiring such facilities to undergo a major renovation to undertake thenew composition's production.

4. Summary of Invention

It has been discovered that a composition consisting essentially of aunique combination of synthetic binders selected for their ability toestablish a permanent bond in the dry state, combined with an expandedmineral (e.g., Perlite and crushed Perlite), organic binding adhesives,drying agents, and hardeners, all contained within a covering of treatedmoisture and heat resistant paper material, produces an improvedlighter-weight, strengthened wallboard product. The technology of thepresent invention utilizes an expanded mineral which physically becomespart of the composite matrix due to the complex formulation of bindersattaching themselves to the mineral, instead of the mineral only actingas a filler. In comparison to the 1 to 10 percent of mineral fillerpreviously utilized in gypsum wallboard, the expanded mineral canincorporate anywhere from 13 to 60 percent of the core composite of thepresent invention, thus dramatically decreasing the amount of gypsumrequired to makeup the core.

Numerous significant improvements have been made available through theimproved wallboard of the present invention. First, the wallboardcomposition of the present invention enables a significant reduction ofthe amount of calcined gypsum required to produce the wallboard. Thisreduction in the amount of calcined gypsum stucco (through the use ofperlite in the wallboard composition) in the method of the presentinvention expands the production capabilities of current wallboardmanufacturing plants. Typically, the gypsum plants are limited incapacity production due to grinding of the gypsum ore or in calcinationof the synthetic gypsum. Stretching the amount of gypsum required whilereducing the energy and overall cost required greatly enhances themanufacturing production capabilities of the modified wallboardmanufacturing facility of the instant invention.

More particularly, calcining equipment and gypsum supply havehistorically been the limiting factors in the production capacity inwallboard manufacturing facilities due to grinding limitations orcalcine kettle limitations. Enlarged milling capacities becomeincreasingly expensive as the gypsum calcining equipment is enlargedand/or improved in newer gypsum plant production. Typically, a standardwallboard manufacturing facility has one calcining operation supplyingeach wallboard production line. Additionally, the current domesticgypsum ore demand far exceeds the present supply; thus, the ability tospread the current gypsum ore supply and decrease the amount of gypsumgrinding required in the present invention improves the productioncapacity of the wallboard manufacturing plant. Also, the presentinvention enables gypsum wallboard manufacturers to reduce the amount ofcalcined gypsum required to run a single boardline, and utilize theircurrent single boardline gypsum supply to operate additional wallboardproduction lines, thus greatly increasing the production capacity of agiven wallboard facility. As a result, the expense of purchasingadditional expensive calcining milling equipment to increase productioncapacity is reduced.

A second benefit of the lightweight technology of the present inventionallows for a wallboard composition that is significantly lighter inweight (up to fifty percent lighter) than current traditional heavygypsum wallboard formulations. This reduced weight also results intransporting lighter loads, in turn reducing transportation costs.Further, job site labor costs are reduced by enabling the workers tohandle lightened loads, such that the installation process is madeeasier and less costly. Similarly, the potential for heavy wallboardrelated injury accidents to the tradesmen that install the wallboard arereduced.

Yet another benefit of the strengthened wallboard of the instantinvention is the reduction in the amount of board breakage and lossesdue to manual or machine transport to the installation site, due to thefact that the composition of the instant invention provides thewallboard with greater flexibility than has been known in previouswallboard compositions.

Still further, the wallboard composition of the instant inventionexhibits equal or greater strength than current heavy gypsum wallboard,with improvements in moisture resistance and flame resistance thatexceeds current industry standards. This lightweight and strength factorequates to decreased structural support load bearing and lessens thetotal support strength required in any project, in turn further reducingoverall construction costs.

The specific constituents of the wallboard core (as set forth in detailbelow) have been found to improve upon the overall structural strengthof the wallboard, lighten its weight, decrease the amount of airborneparticulates during breakage, decrease its brittleness, and expand itsflexibility. Further, the high quality wallboard composition of thepresent invention is completely cost effective to manufacture usingtypical existing wallboard manufacturing equipment and practices withlimited minor modifications and additional equipment, as furtherdescribed herein.

The attempted addition of synthetic binders in the past to wallboardcompositions have reduced the ability to cut the finished wallboardsheet during installation with a utility knife. However, the compositionof the instant invention was developed after several hundred tests andanalysis of numerous chemical combinations, with extensive chemicaltechnical research and testing to realize a brittle cross-linkingcomplex polymer that combines and fuses with the mineral and expandedmineral, that is easily cut and snapped with a utility knife as appliedin standard construction industry use. Further, there has not previouslybeen available a lightweight, strengthened, and re-engineered wallboardproduct formulated with minor low cost changes in the manufacturingprocess that is environmentally friendly and cost effective to produce.

Optionally, reinforcing fibers, fire retardants, water repellents, andother water proofing materials may be part of the composition. Further,the technology of the present invention allows for decreased set timesfrom the pin mixer to the knife in laboratory testing, which in turnincreases boardline manufacturing speeds far beyond what is currentlybeing realized. As manufacturing speeds increase, so does production,enabling greater amounts of wallboard to be produced to meet the currentdemand. This complex formulation of binders can be seen to be utilizedin a wide variety of other building materials as well.

The paper covering or veneer of traditional gypsum wallboard consists ofwastepaper constituents that include, but are not limited to, wastenewspapers, old corrugated papers, kraft cuttings, and flyleaf shavings.As a result, there are wide variants in wallboard covering colorationwhich include brown, tan, grey, pink green and grey-white colors.Additionally, traditional gypsum wallboard strength is largely dependenton the strength of the covering paper, as evidenced by the dependence ofthe results of the flexural break strength and nail pull resistancetests (according to ASTM C-473) on paper fiber strength. Optionally, thepresent invention provides increasing break strength of the papercovering sheets by increasing fiber length and/or by altering the topply by utilizing a paper laminate which provides consistent off-whitecolorization.

The improved, strengthened core material of the instant invention alsoprovides increased compression, shear, and tension loading test resultsin comparison with the conventional non-reinforced gypsum drywall. ASTMTest Standard C79 standard specifications for gypsum sheathing boardrequire that specimens shall surpass an average surface water absorptionof not more than 1.6 g after 2 hours of elapsed time (Section 5.1.7).While gypsum wallboard is required to meet the above ASTM standards,moisture resistance and adverse weather conditions have been long-termproblems with gypsum drywall. The improved wallboard of the instantinvention comprises an improved moisture resistant cover and corematerial that far surpasses ASTM C79-5.1.7. Thus, the present inventionimproves the structural strength, moisture resistance, and weightfactors in the design of a new wallboard or ceiling board to be utilizedas a construction material, whereby gypsum is not the primary coreingredient.

A preferred embodiment of the invention is further directed to a methodfor producing expanded Perlite wallboards of a thickness not less than ¼inch and not greater than 1 inch comprising the steps of: adding starch,boric acid, foamer, gypsum, and a latex vinyl acetate emulsion withwater to expanded Perlite to form a composition; the aqueous slurry ofsettable Perlite is enveloped between two high quality paper coversheets comprised of recycled virgin pulp and formed into a board;directing the continuous board away from the forming apparatus to acutting knife where it is cut to desired length; and finally drying theboard in a high temperature kiln at temperatures ranging from 75° C. to325° C. Optionally, the process further includes the steps of forcinghot air to an encapsulated section of board line, starting the curingprocess prior to the board reaching the board cutting knife.

As previously mentioned, gypsum board manufacturing is a complex processfrom the collection of the gypsum rock to the production of thecompleted wallboard. However, the improved wallboard product of theinstant invention, as described more fully in the examples below, offersincreased wallboard production capacity from a given gypsum supply overtraditional gypsum wallboard products and methods of manufacture.Optionally, when gypsum is not utilized in the wallboard core, theentire calcining system is eliminated from the manufacturing process,and curing temperatures in the manufacturing are substantially reduced.This also greatly reduces the overall production cost of the improvedwallboard of the instant invention.

Yet another improvement of the improved wallboard product of the presentinvention comprises the environmental improvements resulting from areduction of the half-life of the breakdown of the wallboard corematerial. Perlite is a more inert material than gypsum. Thus, it issafer to the environment because it does not react with or leach intoground water. Further, the adhesives used in the wallboard product ofthe instant invention decompose very quickly and easily. Thus, theimproved wallboard of the present invention provides a lightweight,strengthened, fire retardant, whitish-covered Perlite wallboard withenvironmental improvements that is competitively priced to traditionalgypsum wallboard products.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages of the present invention willbecome more apparent from the following detailed description of thepreferred embodiment and certain modifications thereof when takentogether with the accompanying drawings in which:

FIG. 1 is a schematic view of the perlite processing arrangement of theinstant invention.

FIG. 2 is a schematic view of the perlite wallboard production facilityof the instant invention.

DETAILED DESCRIPTION OF THE INVENTION

The strengthened core of the improved wallboard of the instant inventioncontains expanded Perlite in the range of 5% to 60% volume by weight.The expanded Perlite ranges in sizes from 100 to 2000 microns. Thefollowing is a typical sieve analysis of the preferred grade: 3-8%retained on 30+; 30-45% retained on 50+; 25-40% retained on 100+; and15-35% retained on a 100 minus sieve. The preferred grade loose density±1 pound is 6 pounds per cubic foot and has a compacted density of 7.5pounds. The binder consists of a mixture composed primarily of one ormore of the following chemicals: Vinyl acetate polymer, liquid plasticssuch as urethanes and polyurethanes, acrylic polymer, water-basedmodified aliphatic polymers, water soluble sodium silicates solutions,water-based polyvinyl chloride solutions, and polyvinyl alcohols. Dryingagents such as potassium sodium aluminosilicate, Purmol, or fine silicawere also used to quickly drive off moisture. Isopropyl alcohol was alsoused in place of water as a liquid mixing agent. Through the use of theabove listed chemicals, the core was hardened and stiffened, enablingthe improved wallboard to cut more easily and cleanly than typicallyfound with traditional gypsum drywall.

The preferred composition of the improved wallboard product of thepresent invention includes a starch, boric acid, vinyl acetate, andgypsum. It has been found that this combination (in the proportions setforth below) offers the best results for weight, strength, setting andbond of all the examples listed. After applying and analyzing a widevariety of adhesives by themselves and in combination with one another,it was determined that a binder having this composition would allow thewallboard to perform as closely to what is currently used while addingstrength and reducing weight. While gypsum remains an optional elementof the improved wallboard of the instant invention, and therefore is notessential to the production of a functional wallboard product, its usein the composite core of the wallboard of the instant invention doesprovide several unforseen benefits. One such unforseen benefit is thecreation of a product that can be applied in the same manner as iscurrently practiced for the manufacture of traditional gypsum wallboard,using the same tools of the trade and the same techniques by existingtradesmen. Further, gypsum improves the cutting or snap characteristicsof the board of the instant invention, as well as adding to the board'sflexibility. Although gypsum is not crucial to the strength of theimproved wallboard of the instant invention, it adds to the overall bondcharacteristics of the binder. The combination of starch, boric acid andvinyl acetate in itself is sufficient to bond the Perlite together inproducing the composite core of the instant invention. However, theaddition of gypsum into the formulation of the improved wallboardproduct of the instant invention, in comparison to other cementiousmaterials, became preferred due to excellent compatibility of the fourcomponents listed above.

Still another benefit of including gypsum in the composition of theinstant invention involves the setting of the board between the formingequipment and the knife. The optional pre-heating system (described indetail below) starts the curing of a “gypsum free core” to provide apre-cut set or hardening of the continuous board prior to the boardbeing cut at the knife. Using gypsum eliminates the need to pre-heat theboard to get a set or hardening sufficient to cut the board without theslurry oozing out of the ends, and creates a hard enough board to behandled by the post knife inverting equipment

Still further, gypsum adds to the fire retardant capabilities of thecomposite core.

In sum, the inclusion of gypsum as a constituent of the composition ofthe wallboard product of the instant invention creates a gypsum-friendlymodification to existing gypsum wallboard manufacturing facilities, andin doing so creates an improved, strengthened, lightweight wallboardproduct that can be completely and easily transitioned into gypsumwallboard manufacturing facilities.

Optionally, an improved wallboard cover material consists of a manilacolored moisture resistant paper face sheet in the range of 40-50 poundswith an altered top ply. In traditional wallboard structuresincorporating a cover material composed of recycled paper pulp, thelength of fibers in the cover material is between ½ and ¾ inches. Theinstant invention, however, employs a top ply sheet composed of virginfibers of 1 inch or greater. While papers incorporating fiber lengths ofgreater than 1 inch have been produced in the past, to the best of theinventor's knowledge, no such virgin pulp has been applied previously tothe top ply cover sheet of a wallboard sheet. Thus, the inclusion ofsuch extended length fibers into the wallboard cover sheet of theinstant invention provides the unforseen and unobvious benefit ofproviding a much stronger break strength than previously known wallboardstructures.

The unique application of the optional spec paper cover sheets of thewallboard of the present invention is completely formed by any wellknown paper forming process. Using 100 percent “virgin stocks” for thetop ply of the face paper cover sheet allows for predictable linerstrength while also eliminating some of the clays and fillers associatedwith current completely recycled wallboard paper. By integrating avirgin pulp top ply with existing recycled wallboard paper plies,increased strength and wet handling characteristics are achieved. First,a paper cover sheet is made generally comprising a multiply sheetmanufactured on a cylinder machine. Conventional sizing compounds areadded to selected vats such as rosin and alum to internally size some orall plies. The plies are removed and laminated to form an essentiallyunitary web of paper. After being dried, the paper is coated with awater emulsion of the synthetic size of the class consisting of certainsubstituted succinic acid anhydrides, certain substituted glutaric acidanhydrides and the reaction product of maleic acid anhydrides with aninternal olefin. This process allows for effective absorption into thebond liner of the core side of the paper to provide a mechanical linkingof the paper to the composite core.

If bituminous or waxy water-repellent materials are used, they comprisefrom about 1.0 percent to about 10 percent of the Perlite weight byvolume. These materials may be applied to the Perlite from molten statesor as emulsions. If silicone emulsions are used, the silicone comprisesfrom about 0.01 to about 2 percent of the Perlite by weight. Thesilicone emulsions may be applied directly to the Perlite as it exitsthe expander (as set forth in greater detail below) by means well knownin the art.

The addition of a calcium sulfate based compound may also act as afiller material. Many of the preferred samples required no calciumsulfate mixture, although some samples have small percentages rangingfrom 5% to 15%.

A compatible fire retardant, such as boric acid, zinc borate,sulfamates, diammonium phosphate, nitrogen compounds, antimony oxide,silica, titanium oxide, zircon and others can be used and comprise fromabout 0.15 percent to about 3 percent by weight of the board. These fireretardants can be added to the formulation by powder or solution duringthe slurry mixing process, and also by spraying onto the paper coveringfor the purpose of fire retarding the laminate covering paper of thewallboard. The examples of applying fire retardants are listed asfollows:

Example 1 (Fire retardant, moisture resistant system): this systemsprays fire retardant solutions directly onto the board as it leaves thecascade sections and enters the take off area of the manufacturingequipment. This is accomplished by using spray heads overhead togetherwith switch activators to trigger the action as the board passes by onthe conveyor. Additives are supplied by storage tanks and pressure typedischarge systems. The additives are sprayed directly on the face paper.

Example 2 (Fire Retardant): another way to apply a fire retardantquality to the paper is to add it in dry form during the Kraftingprocess of the paper's manufacture. Small particle distribution of fireretardant are added to the pulp slurry prior to extrusion into thepaperboard. This allows for the fire retardant to be completelyintegrated into the paper. This fire retardant could be zinc borate,antimony oxide, nitrogen compounds or sulfamates (sulfer compounds).These are all common fire retardants in paper. The moisture resistanceelement must still be sprayed on using the configuration described abovein example 1. Furthermore, the composite core may also be fire retardanttreated during the mixing process with the addition of compatible fireretardants into the slurry during the mixing process.

The binder, which may be organic or inorganic, is especially selectedfor the property of permanent tackiness in the dry state. Preferably, aself-crosslinking permanently tacky polymer, such as a vinyl polymer, isused. Examples of polymers usefull as binders include organic materialssuch as starch and silicates, and inorganic materials such as polyvinylacetate, vinyl acetate, carboxylated vinyl acetate-ethylene, vinylchlorides, urethane, and polyurethanes, with solvents such asdipropylene glycol monomethyl ether, diethylene glycol monobutyl ether,triethylamine, acrylic resins, modified aliphatics, epoxies, polyvinylalcohol, and combinations thereof.

It is important to note that the unique adhesive technology that isdescribed below is completely new and unobvious to the manufacture ofwallboard products. This process adds a synthetic variable into analready well-used natural adhesive formulation of starch and borate. Theoverall result is a binder which, during the wallboard manufacturingprocess, undergoes a chemical change which provides for completecrosslinking between the starch, borate, and synthetic adhesive to forma strengthened web for gripping the Perlite and forming a rigid core.

Currently, Perlite is used as a filler or additive to take up space intraditional gypsum wallboard compositions. However, the instantinvention utilizes the expanded mineral Perlite as part of thecomposite, adding strength to the core as the binder grabs onto thePerlite. Starch and borate are often added to the traditional wallboardcomposition in order to protect the delicate gypsum crystals and toensure proper crystal growth of the gypsum constituent of the wallboardcore as the wallboard is heat treated in a drying kiln at extremetemperatures. However, starch and borate also combine to form a naturaladhesive. When starch is treated with borate, interchange linkages areformed throughout the borate anion structure resulting in modificationsof the physical properties of the polymer system. Traditional gypsumcompositions do not require an additional binder to give the wallboardstrength, but rather rely on gypsum crystal growth brought about by heattreatment of the wallboard in its final manufacturing stage. Thus,traditional gypsum wallboard compositions do not rely on the adhesivenature of the combination of starch and borate.

The wallboard composition of the present invention, however, doesrequire an additional binder. It has been found that adding anotherpolymer, preferably vinyl acetate, to the starch polymer and boric acidenables a cross-linking to occur between the three constituents. Bycrosslinking the synthetic polymer chain with the starch and boratepolymer chain, more extensive chemical changes are brought about. On amolecular scale, the polymer chain branches extend in all directions,attaching to the Perlite and increasing the overall strength of theboard.

By introducing vinyl acetate, polyvinyl acetate copolymer, or a vinylacetate-ethylene copolymer, the resultant complex molecule is muchlarger, extending its various branches in all directions. It is thisdesirable change in the polymeric structure of the molecule to a morehighly branched chain polymer of higher molecular weight that producesan adhesive with increased viscosity, quicker tack, and better fluidproperties. These qualities are crucial to the strength of the mostpreferred embodiment of the invention. Listed below are two mainbenefits of this polymer adhesive system. First, increased flexural andcompressive strength is realized over current gypsum wallboard ASTMstandards. Secondly, the unique polymer adhesive composition of theinstant invention enables a wallboard composition that is up to as muchas fifty percent lighter than current gypsum wallboard.

Vinyl Acetate Polymers (VAP) separately and in combination with theother previously mentioned adhesives are also found to produce veryfavorable test samples and test results. The VAP utilized is a milkywhite liquid, with typical characteristics in the range of a meltingpoint of 32° F. to 39° F., a vapor pressure of 16 mm Hg to 22 mm Hg (68°F. to 70° F.), specific gravity of 1.0 to 2.0, vapor density of fromless than 1 to 1, a boiling point of from 212° F. to greater than 212°F., and the VAP is water miscible. In general, VAP's are hard, brittle,yet tough resins which are found overall to be favorable to thewallboard installation process which requires that the wallboard havethe ability of being cut and cleanly snapped with a common utility knifeafter the board has been scored. Additionally, each of the variousvendor-supplied VAP's that were tested, when combined in the uniquepercentages of gypsum and perlite samples tested, were found to beenvironmentally friendly and not noxious during heat testing. Further,each of the VAP formulations available clearly exhibited the crosslinking with starch and boron (through the use of boric acid), whereby afusion occurred between the minerals and the adhesive composition. It isthus firmly believed that a chemical fusion of organic and inorganicelements in the composition of the instant invention occurs, rather thana mere adherence by the binder to the mineral. Thus, a fusion occurswhich results in a chemically changed binder combination which, whenheated, in turn chemically fuses the wallboard formulation.

It was also found favorable to raise the glass transition temperature(T_(g)) for better fire testing results of the samples tested. A higherfire rating using VAP's would certainly be preferred in wallboardconstruction applications. The T_(g) range from 28° C. to 39° C., withhigher T_(g) being preferred, were examined during fire tests, and yetall were found acceptable. It is firmly believed that higher glasstransition temperatures are attainable with modified VAP's, which inturn yield improved results in fire tests. It has been found that higherdensities with less water emulsion concentrations are attainable, whichis an important factor in lowering polymer transportation costs andultimate costs of the final product. However, it is firmly believed thatchemical formulation of the modified VAP's on the wallboardmanufacturing site is the preferred option.

A series of compounds derived from soluble sodium silicate glasses areknown as sodium silicate. Basic sodium silicates have been used assimple low cost adhesive binders in sand and earth stabilization and inmineral stabilization including sand-based formed structures at leastsince the early Middle Ages. Sodium silicates are used as binders in themanufacture of refractory cements, air setting refractory mortars, andin plastic cements. The amount of sodium silicates varies from a maximumof 20% for refractory mixtures to a minimum of 5% in air settingmortars. Solutions that have many diversified industrial applicationsresult from varying the ratio of SiO₂:Na₂O and the solids content. Theratio of SiO₂:Na₂O controls the bonding strength of this chemical. Thisalso changes the molecular weight of sodium silicate. Normal sodiumsilicate's molecular weight is 212.15 g. The addition of sodium monoxideor silica modifies the molecular weight.

Sodium silicate has a pH range of 11 to 13; 11 for more siliceousliquids and 13 for the more alkaline. The sodium silicates with ratiosmore alkaline than 1.6 are usually too alkaline and tend to crystallize.The more alkaline silicates have higher wetting power, while the moresiliceous ones reduce the tendency to absorb water and allow drying atnormal atmospheric temperatures. By dissolving glass briquettes with hotwater and steam, liquid sodium silicates are produced. To adjust theSiO₂:Na₂O ratio, caustic soda is used.

The application of sodium silicates alone in varying densities andsolutions as a binder with the Perlite types tested in samples providedrelatively low adhesion and lab test results compared with othercompounds. However, when combined with vinyl acetates and liquidplastics, sodium silicates added strength and lowered total adhesivecosts. Liquid sodium silicates provided by OxyChem, grades 40 to 42Heavy, provided the most favorable lab test results. The addition ofOxyChem Sodium Metasilicate Anhydrous, grade S-25 provided improvedcompound mixtures in some instances and shortened drying times.

Modified Aliphatic Polymers when utilized with other compounds providedlower cost and relatively fast-grabbing, fast-setting, high-strengthadhesives that readily attach to and sufficiently coat the crushed orexpanded Perlite particles. The modified aliphatic polymers (MAP) usedin the examples that follow are water-soluble, milky white in color,almost odorless, and in the range of 45% to 47% solids. However, whentested alone (i.e., without being combined with polyurethane), the useof MAP's provided inferior lab test results.

Liquid plastics such as urethane and polyurethane, chemically treatedwith solvents, are utilized as bonding agents and fillers of the Perlitecore. Urethane compounds consist of acrylamate resins (or acryleserolsas an example) reacting with the diphenylmethane-4 or 4-diisocyanesgroups. Polyisocyanates make up the key substances in polyurethanechemistry. The isocyanate group reacts with the Hydroxyl group and theresulting link between the two residues is the urethane group from whichthe name of the whole polyurethane chemistry is derived. The aromaticisocyanates are more reactive than the aliphatic types and they are lessexpensive. Toluene diisocyanate (TDI) is the largest product produced ofall isocyanates. It is usually offered as a mixture of 80% 2,4-isomerand 20% 2,6-isomer, and it is available in other isomer ratios includingthe pure 2,4-compound. Diphenyl-methane-diisocyanate (MDI) is the secondlargest in volume of the diisocyanates produced. The second component ofthe reaction is the hydroxyl group or so-called polyol (amino-terminatedcomponents) side. Low molecular weight polyols are used as chainextenders or cross linkers which greatly influence the high-temperatureproperties of the resulting polyurethanes (PURs) The flexible parts ofthe commercial PURs are the higher molecular weights in the range of 500to 8000. The main class of polyols are polyesters (derived from adipicacid) and polyethers (derived from propylene oxide). The combination ofthe above two main components of PURs in different ratios, with orwithout water or external blowing agents, leads to a broad range ofporosity, density and modulus of elasticity levels, from rubber-likematerials to the more rigid engineering thermoplastics. In the samplestested, several varying types of commercial urethanes and polyurethaneswere applied. However, so long as caution is used to provide the amount(weight percentage) of urethane or polyurethane specifically set forthin the examples below, the selection of a particular urethane,polyurethane, or combination thereof is within the ability of personhaving ordinary skill.

Additionally, two types of solvents may optionally be employed inthinning polyurethane and urethane applications, and in the cleaning ofthe machinery in the manufacture of the wallboard product which are asfollows.

Dipropylene glycol monomethyl ether is a solvent that is colorless andodorless with a molecular formula of CH3CHOH CH2 OCH2 CHOHCH3. It has amolecular weight of 134.18 g; a boiling point of 230° C. (450° F.), andhas a specific gravity of 1.02. In the examples that follow, thischemical is not greater than 13% by weight.

Diethylene glycol monobutyl ether is a solvent that is a colorless,viscous, mobile, hydroscopic liquid with a faint odor. It has amolecular formula of C5H1803. It has a melting point of −68° C., aboiling point of 231° C., an evaporation rate (butyl acetate=1) of 0.01,solubility in water and ethanol, and a viscosity of 5.17 CST @ 25° C.This chemical is stable and incompatible with strong oxidizing agentsand is less than one percent, by weight, in any of the examples listedbelow.

Although not separately listed, each of these solvents are present intrace amounts in any of the examples that employ polyurethane.

It is a significant feature of the instant invention that themanufacture of the synthetic adhesive binder incorporated into theExamples provided below is carried out at the wallboard productionfacility, as opposed to being manufactured offsite and later transportedto the wallboard production facility. More particularly, for thoseexamples below that employ vinyl acetate, the base components of thebinder are acetic acid and ethylene which make up a vinyl acetatehomopolymer, which in turn is polymerized with a vinyl acetate monomer.Thus, the process by which this occurs and the equipment needed toaccomplish the polymerization of the above-listed constituents islocated at the site of the wallboard manufacturing facility tosignificantly reduce costs. It is additionally believed that the makingof polyurethanes, acrylics, polyvinyl alcohol, potassium sodiumaluminosilicate, polyvinyl chloride, sodium silicates or other syntheticadhesives on site will greatly reduce the cost in use of adhesives inwallboard manufacturing.

Compared to the high costs associated with locating synthetic gypsumplants next to power plants, and given present manufacturing laborexpenses at a traditional gypsum production facility, the manufacture ofthe final synthetic binder at the production site exhibits significantreduction in production costs. Traditionally, synthetic wallboard energycosts are significantly reduced through the industry practice ofcontracting with power plants to dispose of some of the waste produce bythe power plant by using it as a constituent of the synthetic wallboard,in exchange for reduced costs in the supply of electricity. Therefore,the energy costs associated with the manufacture of the adhesives at thesite of the wallboard manufacturing facility are significantly reduced.Further, the presence of manufacturing labor at the wallboardmanufacturing facility, which labor can likewise manufacture theadhesives, reduces the total number of employees required to manufacturethe adhesives, once again reducing the overall manufacturing costs. Theadditional development or polymerization of other adhesives manufacturedon site will additionally reduce production costs. The labor and energyrequired to transport the amount of adhesive material needed tomanufacture mass quantities of wallboard from a location other than thesite on which the wallboard is manufactured would not be logistically orfinancially feasible in a large production setting.

Fire Retardant additives to the adhesives, such as the addition of boricacid, reduce the overall flash point of these chemicals and thereforeincrease the fire rating of the core composite. Under fire rating testsamples, the presence of noxious fumes were greatly reduced even to thepoint of being virtually eliminated as the samples moved away from theepoxies and non-water solvent adhesive mixtures. The combination ofvinyl acetates with cementious materials also provided a good fireretardant combination without the addition of boric acid.

The apparatus necessary for implementing the above-described methodcomprises several elements which together take expanded Perlite andcombine it with varying reactants, apply the mixture to a papersubstrate to form a continuous sheet of laminated Perlite wallboard,convey the wet Perlite wallboard along a conveyor while subjecting it toan initial heat treatment as the wet board travels towards a rotarycutting knife, transferring the laminated assembly to a board dryer, andfinally processing the dried wallboard for shipment.

As shown more particularly in the schematic Perlite processingarrangement of FIG. 1, a Perlite expander system is provided ofconventional design. A preferred Perlite expander is readilycommercially available from Silbrico Corporation as model number M-30,although any similarly configured Perlite expander would likewise besufficient. The Perlite expander system comprises a covered hopper car 1which delivers Perlite ore that has been crushed to the sieve sizeenumerated above to a conveyor 2 positioned beneath the hopper car 1.Conveyor 2 delivers the Perlite ore to an elevator 3 which, in turn,transfers the Perlite to an ore storage container 4. When the crushedPerlite is to be processed into expanded Perlite, a reclaim conveyor 5is used to deliver the crushed Perlite to a Perlite ore surge bin 6,which in turn directs the crushed Perlite ore to an ore feeder 7. Orefeeder 7 directs the crushed Perlite ore via a downwardly orientedelongate chute to a four-way Perlite ore splitter 8. At ore splitter 8,the Perlite ore travels further downward through four elongate tubularpassages and into the vertical furnace expanding tube of Perliteexpander 9. As the crushed Perlite is introduced into the verticalfurnace expanding tube of Perlite expander 9, the crushed Perlite is metby compressed air which is heated between 1700 and 2100 degreesFahrenheit. This heating process causes the crushed Perlite material tosoften while the water bound to the Perlite particles rapidlyevaporates, in turn expanding the Perlite ore to between 12 to 20 timesits original size and into a light, cellular particle which is commonlyreferred to as “expanded Perlite.” Once the Perlite has been expanded,the expanded Perlite particles are light enough to travel upward in theair stream within the vertical furnace expanding tube, through a duct 10at the top portion of the expanding tube, and into a cyclone collector11. Within cyclone collector 11, the larger expanded Perlite particlesfall downward and settle into a hopper at the lower end of the cyclonecollector, while the smaller, fme expanded Perlite particles travelupward from the cyclone collector through a duct and into a dustcollector 12 where they settle. Within dust collector 12, the extremelyfine particles (which are generally not useable in the wallboardproduction process) are collected by a fiber filter media within dustcollector 12. The remaining fme particles and the larger expandedPerlite particles from the hopper of cyclone collector 11 are directedto an expanded Perlite storage silo 200, as described in greater detailbelow.

In a preferred embodiment of the present invention, two independentPerlite expansion systems are utilized in order to provide anappropriate supply quantity of expanded Perlite to the wallboardproduction apparatus.

As shown in the schematic diagram of the Perlite wallboard productionfacility of FIG. 2, located at the feed end of each Perlite expansionsystem 100 is a dense phase pneumatic transport system 400 which movesthe expanded Perlite from the Perlite expansion system 100 to aplurality of storage silos 200. A suitable dense phase pneumatic transport system is readily commercially available from Nol-Tec Systems, Inc.of Lino Lakes, Minn. as Transporter model number 201, although anysimilarly configured pneumatic transport system would likewise besufficient. The pneumatic transport system is configured topneumatically convey expanded Perlite from the Perlite expansion system100 to the expanded Perlite storage silo 200, and in turn from thestorage silos to a secondary feed tank 300 located within the wallboardmanufacturing facility. The dense phase pneumatic transport system hasthe ability to fluidize the dry expanded Perlite material using airpressure, and in turn to convey the material to the desired locationusing sealed pressurized tubes. The transport system utilizes relativelyhigh pressure (above 15 psig), low volume air as the force to transferthe granular bulk solids through a pipeline at low velocity, creatingdense packets or slugs of expanded Perlite which travels through theconveyor system without risk of the abrasive expanded Perlite materialdamaging the interior of the conveyor pipeline.

It should be noted that alternate means of conveying the expandedPerlite are available, such as the utilization of a screw type conveyoror similarly configured mechanical conveyance apparatus. However, it hasbeen found that such mechanical conveyance means used in the transportof expanded Perlite in the context of wallboard manufacture incurs asubstantially higher equipment and maintenance cost. Thus, the use of adense phase pneumatic transport system for conveyance of expandedPerlite during the wallboard manufacturing process provides asubstantial improvement over traditional bulk material transport meanspreviously used in the wallboard manufacturing process.

As mentioned above, the dense phase pneumatic transport system 400 isused to transfer expanded Perlite from the Perlite expansion system 100to a plurality of storage silos 200 of conventional design for storingthe expanded Perlite until needed for new wallboard production. Eachstorage silo is equipped with an airslide of conventional design andknown to persons of ordinary skill in the art of dry bulk materialhandling. The airslide directs expanded Perlite from each of the storagesilos to a transition hopper positioned above a second dense phasepneumatic transport system.

The second dense phase pneumatic transport system is used to conveyexpanded Perlite from the storage silos 200 to a secondary feed tank 300inside of the wallboard manufacturing facility. This second dense phasepneumatic transport system is configured nearly identical to the firstdense phase pneumatic transport system, the sole variations in thesystem relating to the conveyance capacity of the respective systems asdetermined by the wallboard production goals of the particularmanufacturing facility. It should be apparent to those of ordinary skillin the art that modifications could readily be made to the precisehandling capacity of each of the pneumatic transport systems in order tomeet the production requirements of the particular facility, such as bymodifying the diameters of the pipelines in the conveyor system or bymodifying the pressure within the pipeline to in turn change thevelocity of the materials being transferred within.

Traditional wallboard production facilities are plagued with the problemof significant production down-time whenever a problem with the rawmaterial processing and storage equipment located upstream of the actualwallboard construction equipment is experienced. Such problems caninclude air pockets or channels within the storage silos which inhibitor prevent the free flow of material, clogged processing lines, andother common material handling problems. In order to prevent the costlylosses that such down time would create, the present invention employs asecondary expanded Perlite feed tank 300 comprising a steel tankpositioned within the wallboard manufacturing facility in generalproximity to the wallboard construction equipment.

It is significant that traditional gypsum wallboard productionfacilities have been unable to dispense gypsum from a single feedercontainer, but instead have been required to direct processed, calcinedgypsum to multiple small storage bins of limited supply capacity suchthat the entire supply in each bin would be consumed by the productionprocess in a single day. The reason for using such an expensive andinconvenient supply system requiring constant replenishment relies onthe fact that calcined gypsum plaster cannot be stored in largequantities as it has a tendency to absorb surrounding moisture, in turncausing premature hardening. Thus, the present improved wallboardconstruction process enables a simplified expanded Perlite supply tankto be utilized as the expanded Perlite lacks the moisture sensitivityand long term storage sensitivity of calcined gypsum.

As the Perlite expanders work to fill the storage silo that is leastfull with expanded Perlite, expanded Perlite from the most full storagesilo is drawn out and directed to the secondary feed tank 300, using aprogrammable logic controller as is well known to those of ordinaryskill in the art. By constantly maintaining at least one full silo andby always keeping the secondary feed tank filled with expanded Perlite,the risk of being forced to shut down the wallboard production line dueto the above-mentioned equipment problems is at least reduced, if noteliminated altogether. The maintenance of a separate, secondary expandedPerlite feeder tank that is constantly maintained with a ready supply ofexpanded Perlite, and positioned adjacent the wallboard productionequipment, enables any such equipment malfunctions in the remainingstorage and pre-processing equipment to be resolved before the supply ofexpanded Perlite has diminished to such a level that it can no longersupply the expanded Perlite to the production equipment. Likewise, inthe event that each element in the pre-processing and expanded Perlitestorage equipment fails, the supply within the secondary feeder tank maybe used to supply the expanded Perlite to the production equipment untilsuch supply is fully consumed or the failure in the pre-processing andstorage equipment is resolved.

The secondary expanded Perlite feeder tank supplies expanded Perlite tothe wallboard fabrication equipment using volumetric feeders to feed thedry ingredients into a continuous auger type blender 550. A suitablevolumetric feeder is readily commercially available from Acrison asModel BDF. It is of note, however, that alternate means may likewise beprovided for directing the dry Perlite to the wallboard fabricationequipment, including the above-described commercially available densephase pneumatic transport system. Further, a suitable auger type blenderis readily commercially available from Acrison as Model Number 350,although any similarly configured blender will likewise suffice. Blender550 in turn conveys the dry components of the wallboard composition to apin mixer 600.

As explained in greater detail below, the liquid constituents 700 of theadhesives are introduced into the pin mixer 600 along with water and afoaming agent for combining with the dry components of the Perlitewallboard.

Continuous pin mixer 600 is of a conventional design, and a suitablecontinuous pin mixer is readily commercially available from Asa BrownBovari (“ABB”) Raymond Ehrsam Operations, although any similarlyconfigured pin mixer would suffice. The continuous pin mixer combinesthe dry components of the Perlite wallboard construction with the foamedadhesives, all of which are metered into mixer 600 at a uniform rate.The resulting homogeneous free flowing mixture is then discharged fromthe continuous pin mixer onto the back side of the face paper, which inturn is delivered to the wallboard assembly line from paper handlingequipment 800 positioned upstream of the pin mixer.

The paper handling equipment 800 is likewise of conventional design, anda suitable paper handling equipment arrangement is readily commerciallyavailable from ABB Raymond Ehrsam Operations, although any similarlyconfigured paper handling equipment system would suffice. The paperhandling equipment arrangement provides the backing and face paper tothe wallboard production line, and generally includes paper roll racksor rotary unwind stands that hold the paper, paper pull rolls thatsupply the paper at a constant speed to paper tensioners which in turnautomatically adjust to apply uniform tension to the paper, papersplicing tables where the end of the paper from a new roll is joined tothe end of a spent roll, paper guides that automatically align twostreams of paper with the boardline and ensure even paper flowdownstream, paper heaters to remove any moisture from the paper, andpaper creasers to prepare the paper so it folds precisely furtherdownstream.

Wallboard forming apparatus 810 comprising an adjustable mud dam/edgerand an extruder-type forming plate or forming rolls all of conventionaldesign are located just downstream of the pin mixer. The adjustable muddam/edger folds the already creased face paper being supplied from thepaper handling equipment into position to receive the glued backingpaper, while establishing the board width and edge configuration. Theextruder-type forming plate or rolls determine the thickness of thewallboard as it enters the conveyor line, and brings the backing paperinto contact with the mixture and gluing it to the folded face paper tocreate the enclosed envelope that holds the free flowing mixture in theshape of a continuous board.

After the free flowing mixture has been applied to the paper, acontinuous, wet wallboard sheet is formed which proceeds along a boardforming line conveyor of conventional design comprising a greenboardforming line section and a live roll section. The greenboard formingline section (shown generally at 900) comprises a flat belt surface withvery closely spaced rolls to provide adequate belt support to maintain aflat board structure as the wet board travels along the board formingline, and generally extends approximately two-thirds of the distancebetween the forming plate or rolls and a cut-off knife 910. The liveroll section (shown generally at 950) extends the remaining one-third ofthe distance, and serves to deliver partially set board to the cut-offknife. The live roll section 950 comprises open rolls which allowexposure of the board face to the air and help the fmal greenboard setprior to cutting. An aligning device of conventional design is alsopositioned ahead of the knife which positions the board to assure asquare cut.

It is important in the wallboard manufacturing process to ensure thatthe greenboard is sufficiently set by the time it reaches the cuttingknife so that the knife is able to make a clean cut through thewallboard without picking up excessive wet substrate material from theboard which in turn could gum up the knife surface. In the examples setforth below in which gypsum is not used as a setting or hardening agentin the composition, in order to ensure that the Perlite wallboard of thepresent invention has reached a sufficiently dry state to prevent thesubstrate from collecting on the knife surface, the Perlite wallboardforming line is preferably provided with an optional initial heattreatment means which directs heat towards the wet wallboard as ittravels from the forming plate or rolls to the cut-off knife. However,another substantial benefit arises from the heat treatment of the wetboard prior to cutting, and that is the significant cost reductionrealized by the reduction in processing times and temperatures requiredto fully set the board within the drying kiln, as explained in greaterdetail below.

In a first embodiment of the heat treatment means, a tunnel 920 isprovided which encapsulates the board line between the forming plate orrolls and the cut-off knife. The tunnel is provided with a series ofinterconnected air ducts 921 along its upper interior surface, air ducts921 being configured to direct hot air directly downward on the wetboard as it travels along the board line. Heat is supplied to the tunnelusing any conventional and readily commercially available air ductsystem which directs heat from the hot air recycling system of thedrying kiln 1200 (discussed in greater detail below) to the duct worklocated at the ceiling of the heating tunnel. Fans are suspended fromthe ceiling of the heating tunnel to direct the heated air from thedownwardly directed air ducts to the board line.

In a second embodiment of the heat treatment means, a series of dryinghoods are positioned over the board line. The hoods are of conventionaldesign for a standard ventilation hood, and generally comprise a wide,open-mouth air duct opening which faces the surface to be heated (i.e.,the board line), and a section of duct work which extends upward fromthe wide, open-mouth air duct opening and which narrows as it rises awayfrom the air duct opening until it reaches the diameter of the remainderof the duct work. Fans are positioned within the air duct to direct theheated air into the ducts and out of the hoods towards the board line.As in the first embodiment, heat is supplied to the individual dryinghoods using any conventional and readily commercially available air ductsystem which directs heat from the hot air recycling system of thedrying kiln (discussed in greater detail below) to the drying hoods.

After the board has traveled along the belt forming and live rolldewatering sections, the continuous wallboard is cut into individualsheets using a rotary cut-off knife 910 of conventional design. Asuitable rotary cut-off knife is readily commercially available from ABBRaymond Ehrsam Operations of Abilene, Kans., although any similarlyconfigured cut-off knife would likewise suffice. The cutting isperformed by two knife blades, each mounted on a rotor, one above andone below the board. When cutting, the rotors run slightly faster thanthe speed of the board line to assure that the knife blades make astraight cut.

Following the cutting of the board by the rotary cut-off knife, theindividual wallboard sheets are directed along a board acceleratorsection (shown generally at 960) of conventional design. A suitableboard accelerator section is readily commercially available from ABBRaymond Ehrsan operations of Abilene, Kans., although any similarlyconfigured accelerating conveyor section would likewise suffice. Theboard accelerator section comprises sets of rolls turning at increasingspeeds to accelerate the cut boards beyond the cut-off knife in order toprovide adequate spacing between boards to allow time for transfer andinversion of the boards to the dryer infeed section of the boardline. Atthe end of the accelerator section, the boards are received by a boardtransfer/inverter assembly 1000 of conventional design. A suitable boardtransfer/inverter assembly is readily commercially available from ABBRaymond Ehrsam operations of Abilene, Kans., although, once again, anysimilarly configured panel transfer/inverter assembly would suffice. Thetransfer/inverter moves the boards laterally at 90 degrees to theboardline while turning the boards face side up and aligning them sideby side before they are introduced into the drying kiln.

Once the boards have been inverted and transferred to the dryer infeedsection of the boardline, a dryer infeed assembly (shown generally at1100) comprising a conveyor directs boards from the boardtransfer/inverter assembly to the multideck infeed section of the dryingkiln. A suitable dryer infeed assembly is readily commercially availablefrom ABB Fläkt Industri Ab of Växjö, Sweden, although any similarlyconfigured conveyor-type feeder system would suffice.

Drying kiln 1200 of the present invention comprises a plurality oftiers, preferably between 12 and 15, of roller conveyors which receivewallboard at the inlet end of the kiln, convey the wallboard through themultiple heating zone drying section, and discharge the wallboard at theoutlet end of the kiln The basic configuration of the drying kiln is ofconventional design and well known to those of ordinary skill in theart, and a suitable board drier kiln is readily commercially availablefrom ABB Fläkt Industri Ab of Växjö, Sweden. The preferred drying kilnof the present invention comprises a two heating zone kiln ofconventional design. It is significant, however, that the use of Perliteas the primary constituent of the wallboard of the present invention andthe process of providing an initial heat treatment of the wet boardprior to cutting allows the drying process to be carried out atsignificantly lower operational temperatures within the drying kiln.These lower operational temperatures provide a significant cost savingsin both energy consumed in the drying process and in premature wear inthe components of the dryer itself caused by long term exposure toextreme operating temperatures.

As mentioned above, the heat supplied to the optional heat treatmentassembly over the wet board line is supplied by tapping the hot airrecycling system of the drying kiln. As shown in FIG. 2, in aconventional wallboard drying kiln configuration, stacks 1210 whichcomprise a flue or exhaust pipe extending upward from the kiln andthrough the roof of the manufacturing facility are located at each endof the drying kiln to enable moisture laden hot air to escape from theinterior of the kiln. The release of this moisture aids in theevaporation process to drive off the excess water that is present in thewallboard product. As the air rises in the stack, a portion of the airis captured through side ducts located in the sidewalls of the stacks.The side ducts are provided with fans which direct at least a portion ofthe rising air into the ducts which in turn direct the captured air to acondenser. The condenser recaptures the moisture from the air, and thenow dry air is returned into the air inlet 1220 of the drying kiln. Sucha hot air recycling system is well known to those or ordinary skill. Thepresent invention redirects the heated dry air exiting the condenserthrough duct work of conventional design to the optional heat treatmentapparatus situated above the board line, as explained in depth above.

Following the drying stage, the fully set Perlite wallboard exits thedrying kiln via a dryer outfeed system 1300 of conventional design Asuitable dryer outfeed system is readily commercially available from ABBFläkt Industri AB of Växjö, Sweden, although any similarly configuredconveyor-type outfeed system would suffice. The dryer outfeed system inturn directs the Perlite wallboard to dry wallboard handling apparatus,including a transfer-booker 1400, a board bundler 1500, and a boardstacker 1600.

A suitable transfer-booker 1400 of conventional design is readilycommercially available from ABB Raymond Ehrsam Operations of Abilene,Kans., and is used to move each pair of boards off of the dry endboardline onto a receiving table supported by a plurality of rolls,which rolls drop away to allow a series of belts to rotate the board by90 degrees. Hydraulically actuated arms then lift opposing ends of eachpair of boards such that the boards are brought together face to face toprotect the smooth outer surfaces of the wallboard from damage duringhandling, storage, and shipping.

The paired or “booked” boards are then directed to a board bundler 1500of conventional design which squares and aligns the pair of boards,trims them to precise finished length, and tapes the ends. A suitableboard bundler of conventional design is readily commercially availablefrom ABB Raymond Ehrsam Operations of Abilene, Kans.

Finally, after the wallboards have been bundled, they are transferredvia a board stacker assembly of conventional design to a mechanism whichautomatically aligns the bundles and places them one upon another suchthat the bundles may be lifted and carried by a forklift to a storagelocation. A suitable board stacker assembly of conventional design isreadily commercially available from ABB Raymond Ehrsam Operations ofAbilene, Kans.

It is significantly of note that several of the above-identifiedelements used in the process of manufacturing Perlite wallboard as setforth in this specification are likewise in use in current gypsum boardline equipment. Thus, the present apparatus not only provides a new andunique system for manufacturing Perlite wallboard, but also provides ameans by which an existing gypsum wallboard manufacturing facility maybe easily and readily transformed into a Perlite wallboard manufacturingfacility. Thus, by making minor modifications to a traditional gypsumwallboard production facility, and by adding the additional equipmentlisted above (e.g., secondary expanded Perlite feed tank, adhesivesstorage equipment, mixing equipment, and the optional initial heattreatment tunnel and duct work interconnecting the heat treatment tunnelto the standard kiln air recycling system) to an existing gypsumboardline, an existing gypsum wallboard manufacturing facility may besmoothly and economically transitioned into a manufacturing facility forthe improved wallboard of the instant invention, without the investmentcosts of building an entirely new production plant.

EXAMPLES

Wallboard samples were prepared to evaluate both replacing part of thegypsum currently utilized in a conventional formulation process, andreplacing gypsum as a whole in wallboard manufacturing. The gypsum-basedcore was replaced or supplemented with expanded minerals (e.g.,Perlite), adhesives, curing agents, retardants, and fillers. Smallquantities of cementious materials in the range of five to twentypercent added structural strength. Yet, quantities of cementiousmaterials over ten percent added appreciable weight to the Perlite basedcore. Approximately ten (10) percent of a calcium carbonate basedcompound or equivalent added density and continuity to the core whilemoderately increasing structural strength. Lighter weight stucco calciumsulfate based material provided similar results with a reduction inoverall weight of the samples tested. Some adhesives and fillers werefirst mixed together while others were mixed directly with otheringredients. Hundreds upon hundreds of differing combinations of reducedamounts of gypsum and Perlite cores of differing densities and sizesalong with adhesives and the other additives previously mentioned weretried and tested. Differing moisture resistant and fire retardant covermaterials were applied once a favorable core composite was found. Theresultant examples that follow proved to bring very favorable testresults.

Example 1

In the first example, the expanded Perlite of horticulture grade qualitywas supplied from Redco II in California. Five percent to 40% ofmodified aliphatic polymer and from 1% to 40% of the polyurethanecompound were mixed together, then from 5% to 15% of the calcium sulfatebased mixture was added and thoroughly blended. A nearly fifty-fiftyblend of the aliphatic polymer with the polyurethane compound in thethirty to forty five percent range proved to provide the best testresults. Five percent to 50% of the smaller sieve-sized expanded Perlitewas then added to the mixture to form a thick slurry before beingcombined with 5% to 35% of the expanded Perlite and thoroughly mixed.This then formed the new lightweight, strengthened Perlite core for thewallboard.

Ingredient Amount, wt. % Preferred, wt. % Modified aliphatic polymer5-40% 17.5% Polyurethane 1-40% 23.5% Calcium Sulfate 5-15% 11.5%Expanded Perlite 5-50% 17.6% Small sieve expanded Perlite 5-35% 29.9%

The mixture was then formed and heated to 170° C. over a one-hour periodto remove moisture. Heating in the laboratory oven was applied at aconstant temperature; however, forced hot air provides an even betterresult over a shorter period of time. The addition of five percent orless of a curing agent cut the drying time nearly in half.

The Perlite wallboard cover material consists of a whitish, moistureresistant paper in the range of 20-24 pounds with a plastic polymercore. The paper is then treated with a fire-retardant spray similar toZynolyte high temperature spray 1200° F.

During laboratory testing, the Perlite samples were struck with aframing hammer and typically exhibited damage to only one side of thesample. Typical gypsum wallboard would have fractured into numerouspieces while allowing the hammer blow of same pressure to penetrate bothsurfaces. The expanded Perlite core of the wallboard absorbs the impact,cushioning the blow and centralizing the damage in the area around thehammerhead. The blow is further cushioned by applying apaper-plastic-paper laminate in the 11 to 24 pound range to cover thePerlite based core.

Example 2

Ingredient Amount, wt. % Preferred, wt. % Vinyl acetate 1-40% 20.0%Polyurethane 1-40% 28.5% Potassium sodium 5-15% 7.0% aluminoscillatePerlite, expanded 5-50% 28.5% Perlite, fines 5-35% 16.0%

In the second series of samples, total elimination of the calciumsulfate based mixture was analyzed. Additional synthetic adhesivescombined with vinyl acetate forming new compounds replaced the calciumcarbonate based mixture with impressive results. One specific examplecombined vinyl acetate with a liquid polyurethane mixture and then addedsynthetic potassium sodium aluminosilicate as a curing agent. In thisexample the liquid adhesives (vinyl acetate and polyurethane) were mixedtogether first. The dry ingredients, including the Perlite types and thecuring agent (potassium sodium aluminosilicate) were mixed togethersecond, and then the liquid adhesives were folded in third. As describedin Example One, crushed and expanded Perlite were combined from samplessupplied by the Pennsylvania Perlite Corporation in CentralPennsylvania. There were noticeable differences in the various sizes ofPerlite received, which resulted in a large improvement in the weight,texture, and strength of these samples. The addition of the plasticadhesives greatly improved the amount of airborne particulates ascompared to typical gypsum board when cut or scraped through the coresurface. Specifically, a 12″ by 3″ by ½″ sample tested included 2 ouncesof lentil-size expanded Perlite, 0.53 ounce of 30Y expanded Perlite,0.52 ounce of 24Y expanded Perlite, 2 ounces of polyurethane mixture,1.5 ounces of vinyl acetate, and 0.5 ounce of potassium sodiumaluminosilicate. This sample cured well at 160° C. for a one-hourperiod, with a resultant edge hardness of 20.9 lbf, exceeding the ASTMC473 standard of 11 lbf. As in example 1, a hammer blow penetrated butone side of the sample, limiting the impact area of the hammer head tothat area around the hammer head. This sample was also covered by alaminated paper, which assisted in lessening the impact of the hammerblow, thus limiting the depth of impact to only one side of the sample.However, edge hardness depends on the core composition, not the bondingpaper veneer.

Example 3

Ingredient Amount, wt. % Preferred, wt. % Portland Cement 5-15% 10.0%Vinyl Acetate 1-40% 13.3% Polyurethane 5-40% 16.6% Perlite, expanded5-50% 20.0% Perlite, fines 5-30% 13.3% Water 5-50% 26.8%

In the third example, the addition of Portland cement was added to theother adhesives to increase compressive strength and for the purpose oflimiting the wallboard's flexibility. A series of 6×6×½-inch sampleswere prepared with the known light adhesive compounds used in previousexamples, namely, vinyl acetate and polyurethane. While the weight wasincreased by the addition of the Portland cement, the overall strengthwas also increased. A nail-pull resistance test, according to ASTM C473,was conducted and yielded a result of 77 lbf. A noticeable increase inedge hardness was also realized and tested according to ASTM C473, witha resultant edge hardness of 34.0 lbf, exceeding the ASTM C473 standardof 11 lbf for a half inch sample. The addition of adhesives with thePortland cement greatly decreased the air borne particulates as comparedand typically found in cutting or sanding gypsum wallboard. An excess ofgreater than 11% of Portland cement by weight inhibited the ability tocut the material in a manner consistent with cutting typical gypsumwallboard. Also, synthetic plastic cement was tried exhibiting moreimpressive bond strength with the adhesives, yet the overall structuralstrength was lessened by as much as 50% over the use of Portland cement.In all of these samples tested, no gypsum-based material was added orneeded to pass the minimum ASTM requirements for gypsum wallboard.Flexibility versus hardness of the material, including hammer blows tothe wallboard, was analyzed by inspection comparison to typical gypsumwallboard. Again the similar manual framing hammer blows were localizedaround the hammer head in the Perlite wallboard, and were in most everyinstance restricted to penetrating only one side of the material. Thegypsum ½ inch regular wallboard was brittle and the same type hammerblows penetrated through the gypsum wallboard in many instances. Theabsence of the Portland cementious material, or the like thereof, allowsfor more flexibility in the wallboard, thus keeping it from breakingproperly when scored, yet it produced an average of 30% or more lowerflexural strength results. Thus, in this example, improvements to the“cut and snap” and overall 30% or more flexural strength increaseoccurred with the addition of an approximate 10% weight increase, byadding Portland cementious material to the Perlite wallboard samplestested.

Example 4

Ingredient Amount, wt. % Preferred, wt. % Perlite 5-50% 25% Vinylacetate 1-40% 30% Portland cement 5-15% 10% Water 5-50% 35%

In this example, lower amounts of Perlite were used; about 25%, andincreased adhesives and water were used. These were a vinylacetate-based adhesive of about 30% and Portland Cement of about 10%with the remainder being water of about 35%. The mixture was a very wetslurry and was poured into a form and heated at 170 degrees centigradefor one hour. The increased water content entrains air into the slurry,resulting in a much lighter sample. This sample was completely devoid ofcalcined gypsum or calcium sulfate. The resulting weight difference overprevious samples is significant, namely, about 20%. The sample scoredfavorable test results, but were not as high as previous samples with agreater density and was not as strong.

Example 5

Ingredient Amount, wt. % Preferred, wt. % Perlite, Expanded 5-50% 17.5%Perlite, Fines 5-50% 17.5% Sodium silicate 5-40% 30%   Polyurethane1-40% 10%   Water 5-50% 25%  

In this example, two different grades of Perlite from PennsylvaniaPerlite Co. were used, a concrete grade and a Pff24 grade. Sodiumsilicate, about 30%; polyurethane, about 10%; and the remainder beingwater, about 25% were added to about 35% Perlite, making 100% of aslurry. This mixture in slab form was heated to 170 degrees centigradefor 30 minutes to remove excess moisture. Once cooled, this sample (aswith previous samples) was covered with laminated material and preparedfor testing. These ASTM tests are comprised of flexural, compression,tensile, and edge hardness to meet or exceed current gypsum-basedwallboard standards. In all of the above samples, test results farexceed gypsum wallboard ratings.

Example 6

Ingredient Amount, wt. % Preferred, wt. % Perlite, expanded 5-50% 30%Calcium sulfate 5-40% 23% Polyvinyl chloride 1-15%  5% Water 5-50% 42%

In this example, the first step was to mix about 30% commercial Perlitewith about 23% calcium sulfate, and the balance being a 5% solution ofpolyvinyl chloride emulsion in about 42% of water making 100% of aslurry. The mixture was then poured into a form and let set for about 10minutes, becoming fairly hard, and was then heated at 130 degreescentigrade for one hour. The intent was to form a plastic PVC webthroughout the composite matrix during heating after the plaster hadset. Once cooled, this sample was fairly hard and dense but was 40%lighter than the (gypsum core) control sample. Test results showed thatvinyl acetate still scored higher than less preferred binders such aspolyvinyl chloride.

Example 7

Ingredient Amount, wt. % Preferred, wt. % Perlite 5-50% 25% Starch.001-15%  8% Boric acid .001-0%  2% Calcium sulfate 5-40% 10% Vinylacetate 1-40%  5% Water 5-50% 50%

This example discloses a composition reflecting the most preferredembodiment of the improved wallboard composition of the instantinvention, and continues the study of the addition of small percentagesof calcium sulfate into the composite core. It is also a test of anadhesive formulation comprising vinyl acetate polymer emulsion, modifiedstarch, and boric acid. In this test, the first step was to mix about25% Perlite of which 50% or more of said Perlite is in the 10-50 sievesize range, and smaller sized Perlite which nearly 3% passes through a100 mesh sieve. The Perlite (25% by weight) was combined with 8%modified starch, 2.5% boric acid, and about 10% calcium sulfate. Next,about 5% vinyl acetate emulsion was added to about 50% water. The wetand dry ingredients were then combined and mixed for about thirtyseconds. The slurry was then poured into a form with a paper coveringinserted onto it. After the slurry was leveled, the top of the paperenvelope was laid on top. The sample set up fairly hard in about threeminutes. The sample was then removed from the form and heated at 160° C.for about an hour. Once cooled, the sample was weighed and measured andthe results were catalogued. Several days later this sample wasconditioned and then tested to ASTM C473 standards. Test resultsconfirmed nearly double those of the gypsum core control sample in nailpull resistance, edge hardness, and with improved flexural strength.

Example 8

Ingredient Amount, wt. % Preferred, wt. % Perlite 5-50% 35% Starch.001-15%  8% Boric acid .001-10%  2% Vinyl acetate 1-40%  5% Water 5-50%50%

In this example, the same formulation used in example 7 minus the 10%calcium sulfate was used The resulting weight difference was made upwith Perlite. The same procedure was used except the sample was notremoved from the form. This test confirmed the need to preheat theboardline prior to the knife in order to harden the board and to startthe curing process at an earlier stage in formulations void of calciumsulfate, as set forth in greater detail above.

Example 9

Ingredient Amount, wt. % Preferred, wt. % Calcium sulfate 20-60% 47.18%Starch .001-15% 0.353% Raw gypsum accelerator .001-5% 0.314% Potassiumsulfate .001-5% 0.57% Boric acid .001-10% 0.094% Vinyl acetate 1-40%6.29% Ethoxysulfate .001-3% 0.580% Water 5-50% 45.032%

This example discloses the addition of the unique adhesive formulationof the instant invention into traditional gypsum wallboard without anexpanded mineral added. Calcium sulfate, starch, raw gypsum, potassiumsulfate, and boric acid were combined in the above amounts. Then,Ethoxysulfate, vinyl acetate, and water were combined and mixed into afoamy consistency and combined with the dry ingredients. The mixture wasmixed at high speed and then poured into a form with a wallboard paperinsert and sealed and formed into a sheet identical to traditionalgypsum wallboard The sample was then removed from the form and the setwas timed. After timing the set and allowing the full hydration set tooccur, the sample was then heated in a kiln at 180° F. to evaporateexcess water. Once dry, these boards were left to cure for two days andthen tested. These experiments were conducted to evaluate increasedstrength in traditional wallboard compositions with the addition of thesynthetic binder. Set time to the knife was decreased by 25% overall,and nail pull resistance, edge hardness, and flexural strength wereincreased 150% in all the samples that were made and tested. Thisdecrease in set time and increase in strength of the wallboard can allowfor increased operating speeds in current wallboard manufacturingfacilities. Varying curing temperatures were applied in this examplefrom 75° C. to 352° C. with favorable test results. However, thepreferred curing temperatures ranged from 79° C. to 275° C.

Example 10

Ingredient Amount, wt. % Preferred, wt. % Perlite 11-47.5% 13.429%Calcined Gypsum 0-40% 29.082% Starch 0.001-15% 0.894% Ball MillAccelerator 0.001-5% 0.357% Pot Ash 0.001-5% 0.178% Boric Acid 0.001-10%0.134% Vinyl Acetate 1-40% 9.080% Soap Water 1-30% 15.527% Lignosite0.001-3% 0.026% Water 5-50% 31.293%

In this example, first the dry ingredients were combined together andblended until a homogeneous mix was achieved, these dry ingredientsbeing plaster grade expanded perlite with a loose density of 6 to 8pounds per cubic foot, calcined gypsum stucco, starch, ball mill landplaster accelerator, pot ash and boric acid. Secondly, the dry lignositedispersant was combined with the water and mixed until blended. Thirdly,the soap water and vinyl acetate were combined together and blended withan electric mixer to generate foam or bubbles. The soap water and vinylacetate foam mix was then added to the lignosite and water and then allthe wet ingredients were combined with the dry blended ingredients andmixed by hand for about 15 seconds to achieve 100% of a slurry. Theambient temperature was 82° F. and the surrounding humidity was 29%.This slurry was then poured into a standard wallboard paper insert orenvelope to make a ½ inch thick wallboard sample measuring 6 inches by 6inches. The back sheet of the insert was then sealed to the face sheetfolds using a starch based drywall edge paste, formed, and then removedfrom the form, and the initial or snap set was timed and recorded. In atypical drywall manufacturing process there are two different sets,first being the initial or snap set, whereas the continuous boardhardens or stiffens sufficiently to be cut into desired lengthsdownstream at the rotary knife. The secondary or hydration set relatesto the complete hydration of the gypsum crystals, meaning the amount oftime sufficient to rehydrate the calcined gypsum, replacing the twomolecules of H₂O removed during the calcining process of land plaster.This secondary hydration set can be from as low as 4.6 minutes to ashigh as 7 minutes depending on the grind and purity of the land plasterbeing utilized. When higher quantities of the synthetic binder wereadded, the resulting set times were reduced even to the point of settingbefore the mix could be poured into the paper insert envelope, thelowest being recorded at 30 seconds. This is substantially less thancurrent standard drywall snap set times of 3½ to 4½ minutes to theknife. At 2½ minutes the sample of the above example was cut cleanly andinspected. The inspection revealed that the slurry had completelyhardened and it is believed that the chemical reaction of the syntheticbinder (vinyl acetate) and the calcined gypsum allows the gypsum crystalto rehydrate more rapidly than calcined gypsum rehydrated without thesynthetic additive of the present invention. The above process has beenduplicated repeatedly in the lab with slight variations in formulaachieving the same results. A range of volumes of the preferredsynthetic binder (vinyl acetate) were tested with gypsum andconsistently set times were reduced over those of the gypsum controlsamples with no synthetic additives, and consistently stronger sampleswere obtained over those of the gypsum control samples with no syntheticadditives. All procedures including the drying of the samples wereconsistent with typical drywall manufacturing processes. The excesswater in the samples was driven off by placing samples in a laboratorykiln with access to moving heated air at a temperature of between 150°C. and 200° C. for a period of 50 minutes to 1 hour.

I claim:
 1. A wallboard composition comprising: a mineral selected fromthe group consisting of calcium sulfate, perlite, and combinationsthereof; a binder formulation comprising a self-crosslinking permanentlytacky polymer, said binder formulation being selected for its ability tofully cross-link with said mineral; and paper cover sheets sandwichingsaid mineral and said binder formulation therebetween.
 2. The wallboardcomposition of claim 1, wherein said paper cover sheets are formed froma virgin paper pulp comprising fibers having a length of at least oneinch.
 3. The wallboard composition of claim 1, wherein said paper coversheets further comprise fire retardent agent.
 4. The composition ofclaim 3, wherein said fire retardant agent comprises an agent selectedfrom the group consisting of boric acid, zinc borate, sulfamates,diammonium phosphate, nitrogen compounds, antimony oxide, silica,titanium oxide, and zircon.
 5. The composition of claim 4, wherein saidfire retardant agent is present at about 0.15% to about 3% by weight ofthe finished wallboard.
 6. A wallboard composition comprising; a drypowder mineral substrate selected from the group of minerals comprisingcalcium sulfate, perlite, and combinations thereof; a synthetic bindercomprising a self-crosslinking permanently tacky polymer, starch, andborate; and paper cover sheets sandwiching said mineral and said binderformulation therebetween.
 7. The wallboard composition of claim 6,wherein said paper cover sheets are formed from a virgin paper pulpcomprising fibers having a length of at least one inch.
 8. The wallboardcomposition of claim 6, wherein said paper cover sheets further comprisefire retardant agent.
 9. The wallboard composition of claim 8, whereinsaid fire retardant agent comprises an agent selected from the groupconsisting of boric acid, zinc borate, sulfamates, diammonium phosphate,nitrogen compounds, antimony oxide, silica, titanium oxide, and zircon.10. The wallboard composition of claim 9, wherein said fire retardantagent is present at about 0.15% to about 3% by weight of the finishedwallboard.
 11. The wallboard composition of claim 6, wherein saidself-crosslinking permanently tacky polymer comprises vinyl acetate. 12.The wallboard composition of claim 11, wherein said vinyl acetate ispresent at about 1% to about 40% by weight.
 13. The wallboardcomposition of claim 6, wherein said starch is present at about 0.001%to about 15%, and said borate is present at about 0.001% to about 10%.